Electroluminescent device, method of manufacturing the same, and display device including the same

This application claims priority to Korean Patent Application No. 10-2022-0115812 filed on Sep. 14, 2022, and all the benefits accruing therefrom under 35 U.S.C. § 119, the content of which in its entirety is herein incorporated by reference.

The present disclosure relates to an electroluminescent device, a method of manufacturing the same, and a display device including the same.

Semiconductor particles (e.g., semiconductor nanoparticles) having a nanometer size may exhibit luminescence properties. For example, the semiconductor nanoparticles can exhibit quantum confinement effects. Light emission from the semiconductor nanoparticles may occur when an electron in an excited state transitions from a conduction band to a valence band as a result of light excitation or due to an applied voltage. The semiconductor nanoparticle may be configured to emit light of a desired wavelength region by adjusting its size, composition, or a combination thereof.

Semiconductor nanoparticles may be used in an electroluminescent device and a display device including the same due to improved color purity and color reproducibility.

However, improvements in the efficiency and life-span of the device are continuously desired.

An embodiment provides an electroluminescent device that includes semiconductor nanoparticles and has excellent color purity and color reproducibility as well as excellent efficiency and life-span characteristics.

Another embodiment provides a method of manufacturing the electroluminescent device.

Another embodiment provides a display device that includes the electroluminescent device.

In an embodiment, an electroluminescent device includes a first electron auxiliary layer, a first light emitting layer, and a first electrode disposed on a first surface of a transparent electrode; and

The transparent electrode may have a transmittance of greater than or equal to about 90%.

The transparent electrode may be formed in a pattern and may be formed in a direction orthogonal to the patterns of the first electrode and the second electrode.

The zinc oxide nanoparticles may further include an additional metal selected from Mg, Ca, Zr, W, Li, Ti, Y, Al, or a combination thereof.

The zinc oxide nanoparticles may be of a formula ZnMO wherein, M is Mg, Ca, Zr, W, Li, Ti, Y, Al, or a combination thereof, and 0≤x≤0.5.

An average size of the zinc oxide nanoparticles may be about 1 nanometers (nm) to about 10 nm.

A thickness of each of the first electron transport layer and the second electron transport layer may be in a range of about 10 nm to about 90 nm.

The first light emitting layer and the second light emitting layer may include the same or different semiconductor nanoparticles.

The plurality of semiconductor nanoparticles may not contain cadmium, lead, mercury, or a combination thereof.

The plurality of semiconductor nanoparticles may include a first semiconductor nanocrystal containing zinc, selenium, and tellurium, and a second semiconductor nanocrystal containing zinc chalcogenide; where the second semiconductor nanocrystal is different from the first semiconductor nanocrystal.

The plurality of semiconductor nanoparticles may include a first semiconductor nanocrystal containing indium, phosphorus, and, optionally, zinc, and a second semiconductor nanocrystal containing zinc chalcogenide; where the second semiconductor nanocrystal is different from the first semiconductor nanocrystal.

An average size of the plurality of semiconductor nanoparticles may be about 4 nm to about 30 nm.

The plurality of semiconductor nanoparticles may include a core including the first semiconductor nanocrystal and a shell disposed on the core and including the second semiconductor nanocrystal.

The first electron transport layer may be adjacent to the first light emitting layer (e.g., directly on the first light emitting layer), and the second electron transport layer is adjacent to the second light emitting layer (e.g., directly on the second light emitting layer).

The electroluminescent device may further include a first hole auxiliary layer between the first light emitting layer and the first electrode, and further include a second hole auxiliary layer between the second light emitting layer and the second electrode.

In another embodiment, a method of manufacturing the electroluminescent device includes coating a dispersion containing zinc oxide nanoparticles on a first surface of a transparent electrode and then drying to form a first electron auxiliary layer, and coating a composition containing semiconductor nanoparticles on the first electron auxiliary layer and then drying to form a first light emitting layer,

Another embodiment provides a display device includes the aforementioned electroluminescent device.

The display device may include a portable terminal device, a monitor, a laptop computer, a television, an electronic display board, a camera, or an electric component.

The electroluminescent device may exhibit improved external quantum efficiency and life-span characteristics and may solve deterioration problems at interfaces between the first light emitting layer and the first electron auxiliary layer and between the second light emitting layer and the second electron auxiliary layer.

Advantages and characteristics of this disclosure, and a method for achieving the same, will become evident referring to the following exemplary embodiments together with the drawings attached hereto. However, the embodiments should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

In order to clearly explain the present disclosure, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar elements throughout the specification.

The size and thickness of each constituent element as shown in the drawings are randomly indicated for better understanding and ease of description, and this disclosure is not necessarily limited to the embodiments depicted in the drawings. In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. And in the drawings, for convenience of description, the thickness of some layers and regions are exaggerated.

It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. Also, to be disposed “on” the reference portion means to be disposed above or below the reference portion and does not necessarily mean “above”.

It will be understood that, although the terms “first,” “second,” “third” etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer, or section. Thus, “a first element,” “component,” “region,” “layer,” or “section” discussed below could be termed a second element, component, region, layer, or section without departing from the teachings herein. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms, including “at least one,” unless the content clearly indicates otherwise. “At least one” is not to be construed as being limited to “a” or “an.” “Or” means “and/or.”

As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

In addition, in this specification, the phrase “on a plane” means viewing a target portion from the top, and the phrase “on a cross-section” means viewing a cross-section formed by vertically cutting a target portion from the side.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Further, the singular includes the plural unless mentioned otherwise.

Hereinafter, values of a work function, a conduction band, or a lowest unoccupied molecular orbital (LUMO) (or valence band or HOMO) energy level is expressed as an absolute value from a vacuum level. In addition, when the work function or the energy level is referred to be “deep,” “high” or “large,” the work function or the energy level has a large absolute value based on “0 eV” of the vacuum level, while when the work function or the energy level is referred to be “shallow,” “low,” or “small,” the work function or energy level has a small absolute value based on “0 eV” of the vacuum level.

As used herein, the term “Group” may refer to a group of Periodic Table. As used herein, “Group II” refers to Group IIA and Group IIB, and examples of Group II metal may be Cd, Zn, Hg, and Mg, but are not limited thereto. As used herein, “Group III” refers to Group IIIA and Group IIIB, and examples of Group IIIA metal may be Al, In, Ga, and TI, and examples of Group IIIB may be scandium, yttrium, or the like, but are not limited thereto. As used herein, “Group IV” refers to Group IVA and Group IVB, and examples of a Group IVA metal may be Si, Ge, and Sn, and examples of Group IVB metal may be titanium, zirconium, hafnium, or the like, but are not limited thereto. As used herein, “metal” includes a semi-metal such as Si. As used herein, “Group V” includes Group VA and includes nitrogen, phosphorus, arsenic, antimony, and bismuth, but is not limited thereto. As used herein, “Group VI” includes Group VIA and includes sulfur, selenium, and tellurium, but is not limited thereto. As used herein, the average (value) may be mean or median. In an embodiment, the average (value) may be a mean average.

As used herein, when a definition is not otherwise provided, “substituted” refers to replacement of at least one hydrogen of a compound or the corresponding moiety by a C1 to C30 alkyl group, a C1 to C30 alkenyl group, a C2 to C30 alkynyl group, a C6 to C30 aryl group, a C7 to C30 alkylaryl group, a C1 to C30 alkoxy group, a C1 to C30 heteroalkyl group, a C3 to C30 heteroalkylaryl group, a C3 to C30 cycloalkyl group, a C3 to C15 cycloalkenyl group, a C6 to C30 cycloalkynyl group, a C2 to C30 heterocycloalkyl group, a halogen (—F, —Cl, —Br, or —I), a hydroxy group (—OH), a nitro group (—NO), a cyano group (—CN), an amino group (—NRR′ wherein R and R′ are each independently hydrogen or a C1 to C6 alkyl group), an azido group (—N), an amidino group (—C(═NH)NH), a hydrazino group (—NHNH), a hydrazono group (═N(NH)), an aldehyde group (—C(═O)H), a carbamoyl group (—C(O)NH), a thiol group (—SH), an ester group (—C(═O)OR, wherein R is a C1 to C6 alkyl group or a C6 to C12 aryl group), a carboxyl group (—COOH) or a salt thereof (—C(═O)OM, wherein M is an organic or inorganic cation), a sulfonic acid group (—SOH) or a salt thereof (—SOM, wherein M is an organic or inorganic cation), a phosphoric acid group (—POH) or a salt thereof (—POMH or —POM, wherein M is an organic or inorganic cation), or a combination thereof.

As used herein, the expression “not including cadmium (or other harmful heavy metal)” may refer to the case in which a concentration of each of cadmium (or another heavy metal deemed harmful) may be less than or equal to about 100 parts per million by weight (ppmw), less than or equal to about 50 ppmw, less than or equal to about 10 ppmw, less than or equal to about 1 ppmw, less than or equal to about 0.1 ppmw, less than or equal to about 0.01 ppmw, or about zero. In an embodiment, substantially no amount of cadmium (or other toxic heavy toxic metal) may be present or, if present, an amount of cadmium (or other heavy metal) may be less than or equal to a detection limit or as an impurity level of a given analysis tool (e.g., an inductively coupled plasma atomic emission spectroscopy).

“About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations, or within ±10%, ±5%, ±3%, or ±1% of the stated value.

Semiconductor nanoparticles such as quantum dots may exhibit quantum confinement or exciton confinement. In this specification, the term nanoparticle or quantum dot is not limited in its shape unless specifically defined. The semiconductor nanoparticles may have a size smaller than the diameter of the Bohr excitation in the bulk crystal of the same material and may exhibit a quantum confinement effect. The quantum dots may emit light corresponding to their bandgap energy by controlling the size of the emission center of the nanocrystals.

As used herein, the wording “external quantum efficiency (EQE)” is a ratio of the number of photons emitted from a light emitting diode (LED) to the number of electrons passing through the device and can be a measurement as to how efficiently a given device converts electrons to photons and allows them to make an escape. The EQE can be determined by the following equation:EQE=an efficiency of injection×a (solid-state) quantum yield×an efficiency of extraction

As used herein, a maximum EQE is a greatest value of the EQE.

As used herein, a maximum luminance is a greatest value of the luminance a given device can achieve.

As used herein, the wording quantum efficiency may be used interchangeably with a quantum yield. In an embodiment, the quantum efficiency may be a relative quantum yield or an absolute quantum yield, for example, which can be readily measured by any suitable, e.g., commercially available, equipment. The quantum efficiency (or quantum yield) may be measured in a solution state or a solid state (in a composite)

In an embodiment, “quantum yield (or quantum efficiency)” may be a ratio of photons emitted to photons absorbed, e.g., by a nanostructure or population of nanostructures. In an embodiment, the quantum efficiency may be determined by any suitable method. For example, there may be two methods for measuring the fluorescence quantum yield or efficiency: the absolute method and the relative method.

The absolute method directly obtains the quantum yield by detecting all sample fluorescence through the use of an integrating sphere. In the relative method, the fluorescence intensity of a standard sample (e.g., a standard dye) may be compared with the fluorescence intensity of an unknown sample to calculate the quantum yield of the unknown sample. Coumarin 153, Coumarin 545, Rhodamine 101 inner salt, Anthracene, and Rhodamine 6G may be used as a standard dye, depending on the PL wavelengths thereof, but are not limited thereto.

Unless mentioned otherwise, a numerical range recited herein includes any real number within the endpoints of the stated range and includes the endpoints thereof

A bandgap energy of a semiconductor nanoparticle may vary with a size and a composition of a nanocrystal. For example, as a size of the semiconductor nanoparticle increases, the bandgap energy of the semiconductor nanoparticle may narrow, e.g., decrease, and the semiconductor nanoparticle may emit light of an increased emission wavelength. A semiconductor nanocrystal may be used as a light emitting material in various fields such as a display device, an energy device, or a bio light emitting device.

A quantum dot electroluminescent device (hereinafter, also referred to as QD-LED) may emit light by applying a voltage and includes a semiconductor nanoparticle as a light emitting material. A QD-LED uses a different emission principle from an organic light emitting diode (OLED) using organic materials and realizes, e.g., displays, more pure colors (red, green, blue) and improved color reproducibility thereby attracting attention as a next generation display device. A method of producing the QD-LED may include a solution process, which may lower, e.g., reduce, a manufacturing cost. In addition, the semiconductor nanoparticles in the QD-LED is based on an inorganic material, contributing to realization of an increased stability. It is still desired to develop a technology that improves efficiency and a life-span of a device.